1. Field of the Invention
The present invention relates to a rolling die and a method for forming a thread or worm and a spline having a small number of teeth by rolling simultaneously. More particularly, the present invention relates to a rolling die and a method for forming a thread or worm and a spline having a small number of teeth whose number is thirteen or less simultaneously by rolling.
2. Description of the Related Art
Generally, a shaft member having a thread or worm and a spline coaxially is formed by rolling using a thread rolling die for threads or worms and a spline rolling die for splines. The thread rolling die and spline rolling die are disposed to different positions laterally and linearly. In this rolling, the thread or worm and spline are formed by rolling at different timings. Accordingly, the rolling takes long time, and the rolling machine increases in size.
In recent years, for example, as disclosed in Japanese Examined Patent Application Publication No. H01-41419 (lines 20th to 22nd of the 4th column, FIGS. 3 to 6, etc.) and Japanese Patent No. 2902101 (lines 7th to 10th of the 5th column, FIGS. 1 to 4, etc.), a thread rolling die and a spline rolling die are disposed parallel to each other to form a thread or worm and spline simultaneously by rolling.
In the above conventional method, a spline having a small number of teeth whose number is thirteen or less cannot be formed by rolling together with a thread or worm.
In other words, when a small number of teeth are formed by rolling onto a rolled material to form a shape of a gear such as a spline (the number of teeth of the spline is thirteen or less), teeth of a rolling die can be out of contact with teeth of the rolled material. Accordingly, the rolled material cannot be rolled, disabling the rolling.
Conventionally, the spline having a small number of teeth needs to be formed by gear cutting (machining), while the thread or worm is formed by rolling. This is extremely inefficient.
On the other hand, there are a method (the so-called zigzag rolling) in which the spline having a small number of teeth is formed by rolling onto two portions out of phase by a half pitch, and a method in which a rolled material is rolled forcibly by use of a guide block for the rolling. The latter method is disclosed in Japanese Examined Patent Application Publication S60-187. In the former, one of the rolled splines needs to be cut and deleted. In the latter, a portion formed by rolling by use of the guide block needs to be cut and deleted. These are extremely inefficient.